Download Anaerobic Pathways Glycolysis

3/6/2017
Anaerobic Pathways
• Glycolysis
– Glucose + 2 ATP → 4 ATP + 2 Pyruvate
• No oxygen required
• Fairly low energy yield
• Lactate byproduct
– Resting levels low
– Tolerances 40 mmole/kg in humans, 200
mmole/kg in sea turtles
– During strenuous exercise levels highest in muscle
and liver tissue
Glycolysis
• Lactate
– common animal endpoint
– not a waste product
One alternative endpoint is Alanine.
What organism uses that? When?
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Alternate Endpoints
• Some animals use alternate
endpoints under some conditions
– Goldfish use ethanol in cold,
anoxic conditions
– Glucose → pyruvate →
acetalaldehyde → ethanol
– Ethanol is excreted
Gluconeogenesis – fate of end products
• Lactate transferred to liver, converted back into glucose
• Cost of 6 ATP
• Why bother?
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• Source and storage of glucose
• Glycogen – glucose polymer
– Hormone control:
– Insulin - stimulates storage of glucose in glycogen
– Glucagon – reverse (glycogenolysis)
Review of some terms
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Catabolic processes
– Glycolysis
– Glycogenolysis
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Anabolic processes
– Glycogenesis
– Gluconeogenesis
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Molecules
– Glucose
– Glucagon
– Pyruvate
– Lactate
– Creatine phosphate
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Hormones
– Insulin
– Glucagon
How does the Atkins diet “work”?
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Oxygen in the Atmosphere
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Aerobic pathway
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Overview
– Glucose + 36 ADP + 6 O2 →
36 ATP + 6 CO2 + 6 H2O
Glycolysis yields 2 pyruvate
Convert pyruvate into acetylCoA (C2)
Citric Acid cycle
– Combine with Oxaloacetate
(C4) to make Citrate (C6)
– Break off two carbons
(released as CO2)
– Yield (per pyruvate)
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2 CO2
3 NADH
1 FADH2
1 GTP
Electron transfer system
• From Glycolysis, pyruvate
oxidation and Citric Acid cycle
– 1 glucose → 10 NADH + 2
FADH2
• Electrons transferred to O2,
negatively charged oxygen
combines with protons
(metabolic water)
• Protons pumped out of
mitochondrial matrix, setting
up a gradient
• ATP synthase converts ADP →
ATP as protons flow back into
matrix
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Overview, ATP yields
+2
+2
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Alternative Fuels
• Various amino acids can
feed into parts of Citric
Acid cycle
• Recall osmoregulation of
intertidal copepod
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Lipids - (CH2O)3(CH2)3n(CO2H)3
• Common fuel for aerobic
metabolism
• Very high energy density
• Chain of CH2 repeats
• Saturated vs. unsaturated
• Produces Acetyl-CoA (→ Citric
Acid cycle) through β-oxidation.
Lipids - (CH2O)3(CH2)3n(CO2H)3
• Greater oxygen demand to produce ATP, measured as
respiratory quotient (RQ)
• Carbohydrate metabolism
– C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
– Ratio of CO2 to O2 is 1:1
– RQ = 1.0
• Lipid metabolism (n=17)
– (CH2O)3(CH2)51(CO2H)3→ 6 CO2 + 6 H2O
– C57H111O9 + 80 O2 → 57 CO2 + 55 H2O
– Ratio of CO2 to O2 is 57:80 ~ 0.67
– RQ = 0.7
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Comparing fuels
Metabolic water
(g per KJ)
0.032
0.027
0.022
• Carbohydrates
– Fast ATP yield, high ATP per unit oxygen, low
energy density
• Lipids
– Slow ATP yield, low ATP per unit oxygen, high
energy density
Patterns of Energy Use
• The relative contribution of fuel types, duration and
capacity are all variable.
• For example, general categories of muscle differ:
– Red muscle
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Lipid catabolism
High myoglobin, well supplied by vessels
Fatigue resistant
Slow acting
– White muscle
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Carbohydrate catabolism
Low myoglobin
Fatigue quickly
Fast acting
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Ecological Implications
• Short distance, fast flying insects
– Rely on carbohydrates
– Fast start, fast metabolism
– Low duration
• Long distance, slow flyers
– Lipids, more dense energy storage
– Slower to metabolize
• Flying locust energy requirements
– 500 mg per hour glycogen
– 70 mg per hour lipid
– Uses glycogen to initiate flight, switches to lipid
• Migrating salmon
– Begin migration using lipid
stores
– Infrequent burst acceleration
involves carbohydrates
– Later in trip, protein
catabolism
• Humans
– High capacity for carbohydrate
metabolism and lactate
turnover
– Carb-loading - maximize
muscle glycogen stores
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Environment
Glucose
Animal
Glycogen
+2
-6
Diet
Pyruvate
Lipids
Some
alternative
endpoints
Lactate
Acetyl-CoA
CO2
CO2 H2O
Citric Acid +
Electron
Transport Chain
Amino Acids
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O2
Energy Storage
Very Short Term
Low ATP demand, charge system
ATP
Creatine
High ATP demand, supply P
Short Term Storage
High – insulin, glycogenesis
Blood Glucose
Levels
Glycogen
Low – glucagon, glycogenolysis
Long Term Storage
Insulin - lipogenesis
Acetyl-CoA
Lipids
Epinephrine, glucagon - Lipolysis
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